The responses of retinal neurons to light stimulation reflect the interplay between intrinsic cellular properties and the pattern and strength of synaptic inputs. Plasticity at the synaptic level enables the retina to respond continuously under wide variations in ambient light conditions. The proposed research is aimed at understanding the molecular and cellular mechanisms by which two forms of excitatory synaptic transmission in the retina, gap junctions and glutamatergic receptors, are modulated by the neuromodulators DA and NO. The experimental approach combines electrophysiological, biochemical, and molecular techniques to study horizontal cell plasticity at the molecular, cellular, and network levels. Results of the proposed studies should provide new insights and information concerning the molecular and cellular mechanisms of network adaptation, which shape neuronal responses under changing stimulus conditions.